Doctoring devices



Aug. 14, 1962 L MacDONALD DOCTORING DEVICES 2 Sheets-Sheet 1 Filed Jan.6, 1960 fflz enfor [4N Mac Davao Aug. 14, 1962 l. J. M DONALD DOCTORINGDEVICES 2 Sheets-Sheet 2 Filed Jan. 6, 1960 jrzv erzfor [4N Mm:flan/01.0

United States Patent Quebec, Canada Filed Jan. 6, 1960, Ser. No. 735 8Claims. (Cl. 15-256.51)

This invention relates to improvements in doctoring means for theremoval of deposits from the outer surface of a drum which is eitherwholly or partially immersed in a liquid suspension of particles ofmatter.

The conventional type of doctor employed for this purpose ususallyconsists of a long thin blade of suitable material which is secured in aframework so that one of its edges presses against the moving surface ofa drum or cylinder, and so scrapes off any fibrous material which clingsto the surface of the drum of cylinder. When high intensity of loadingis required at the contact of the working edge of the doctor on themoving surface of the drum or cylinder, it is necessary to provide arigid supporting frame which is usually massive in order to be capableof withstanding the forces involved without allowing defiections of theblade which would be undesirable because of the need for continuous andsubstantially uniform doctor blade loading for satisfactory performance.

The present invention proposes to overcome the difficulties anddisadvantages inherent in the conventional type doctoring device. Tothis end it is an object of this invention to provide a means fordoctoring the surface of a body having the surface contour of a solid ofrevolution, which gives a high doctor loading without recourse to abulky supporting structure.

Another object is to provide a means for doctoring a drum surface whichrequires only tensile loading of the doctor' means to achieve loading ofthe doctor edge against the surface to be doctored.

A further object is to provide a means for doctoring of the characterdescribed which is readily adjustable to increase or decrease theloading of the doctor edge against the surface to be doctored.

A still further object is to provide a means for doctoring of thecharacter described which is readily adjustable for quick andinexpensive replacement of a worn doctor.

Still another object of this invention is to provide a means fordoctoring which has a minimum amount of a static surface area on whichdeposits may form.

I The above and other objects and characteristic features of thisinvention will be understood more readily from the following detaileddescription taken in connection with the accompanying drawings, inwhich;

' FIG. 1 is an elevational view of a drum and a doctoring meansembodying this invention.

, FIG...2 is an elevational view of the drum and doctoring means atright-angles to the view shown in FIG. 1.

FIG. 3 is a plan view of same.

FIG. 4 is an enlarged fragmentary view showing one manner in which adoctoring means feeding reel is mounted.

FIG. 5 is a plan view of FIG. 4.

FIG. 6 is an elevational view illustrating modifications of the mountingof the doctoring means.

FIG. 7 is an elevational view illustrating further modifications.

FIGS. 8 to 12 are sectional views, greatly enlarged, illustratingmodified forms of the doctoring means.

Referring more particularly to FIGS. 1 to 3 of the drawings, theinvention in the embodiment immediately to be considered consists of awire or tape 5 wound in a 3,94,874 Patented Aug. 14, 1%62 icesubstantially helical form about the surface of a cylinder or drum 6from one end to the other. The wire or tape, hereinafter referred to asa doctor 5, is fed through a clamping bar 9 on the end surface of abracket 10 adjacent one end of the drum. The doctor is then helicallyformed about the surface of the drum to the opposite end thereof andfrom there it is passed through a second clamping bar 11 on the endsurface of a second bracket '12.

The bracket 10 is an integral extension of a bearing block 14 and hasits clamping end surface lying preferably in a plane tangent to thecurved surface of the drum at the nearest point of contact of the doctorwith the drum surface. The clamping bar 9 is provided with a pair ofbolts 15 which straddle the doctor and are tightened to compress the bar9 against the clamping surface of the bracket 10 with the doctortherebetween. The bearing block 14, which supports one journal 16 of thedrum, is fixed by bolts 17 to two supporting channels 18 which arethemselves supported by suitable means (not shown) in a vat or likecontainer. The journal 16 is connectable to suitable driving means (notshown) which is located beyond the bearing block 14.

The bracket 12 is also an integral extension of a bearing block 20 andhas its clamping end surface lying preferably in a plane tangent to thecurved surface of the drum at the nearest point of contact of theadjacent end of the doctor with the drum surface. The clamping bar 11 isprovided with a pair of bolts 21 which screw into the clamping end ofbracket 12 to secure the doctor between the bar and the bracket end inthe manner abovedescribed in relation to the clamping bar 9. The bearingblock 2t), which supports the journal 22'on the opposite end of thedrum, is shown to be fixed by bolts 23 to a mounting 24 at the bottom ora wall 25 of the vat.

The doctor 5 may be fed from a reel 8 to the clamping bar 9. As will beseen in FIGS. 4 and 5, the reel 8 is mounted on an axle 27 between twoparallel arms 28 which are secured at their inner ends to two adjacentsides of bracket 10. The arms 28 extend outwardly from the sides of thebracket 10 and are laterally offset with respect to the axis of the drumat an angle predetermined bythe angle at which the doctor approaches theend of the drum. The angle at which the doctor approaches the drumaccording to whether the helix angle is small or large, as shown FIGS. 6and 7, and the lateral offset of the real supporting arms 28 withrespect to the axis of the drum will vary according-1y so that thedoctor will be fed from the reel to the drum surface along a line atright angles to the axis of the reel.

FIGS. 6 and 7 show plan views of a doctor with a small helical angle,and of one'with a large helical angle, respectively. The version withthe small angle would be more suitable for application to drums havingconvex surfaces, e.g. barrel shape, and the version employing the largeangleto drums having concave surfaces, e.g.

hour glass shape.

FIGS. 6 and 7 also illustrate modified clamp supports. Here the clampingbars 9 and 11 are mounted on brackets 30 and 31 respectively which aresecured to opposing sides 32 and 33 of the vat. The reel (not shown) mayalso be mounted on similar brackets carried by one side wall of the vatso that the axis of the reel is at right angles to the angle of theapproach of the doctor to the adjacent end of the drum as predeterminedby the helix angle of the doctor about the surface of the drum.

The doctor according to the present invention is quickly and easilyreplaced when worn. This is accomplished by loosening the clamping bars9 and 11, then drawing the doctor from the end remote from the reeluntil a suflicient amount is withdrawn to replace the worn section ofthe 3 7 doctor. When the required amount is withdrawn from the reel thelatter may be locked to prevent further unreeling by means of a lockingmember 35 which engages the reel axle 27. The clamping bar bolts arethen screwed home. After suitable tension is applied along the length ofthe doctor, the clamping bolts are screwed home to secure the doctor inits taut condition at either ends of the drum.

FIGS. 8 to 12 inclusive show cross-sections of modified forms which thedoctor may take. In FIG. 8 the doctor is in the form of a cylindricalwire. FIG. 9 shows the crosssection to be triangular. FIG. 10 shows thecross-section to be that of a broad band. FIG. 11 shows a modificationof the band in which the edges are bevelled to provide a knife edge.FIG. 12 is a modification of the band shown in FIG. 11 in which the bandis transversely curved to conform with the contour of the surface of thedrum at the predetermined angle of helix.

This invention is intended to give high doctor loading, Without recourseto bulky supporting structure which interferes with stock flow and whichwould provide an undesirable static surface area on which fibre depositcould occur. In operation, the doctor and the drum surface have motionrelative to one another. This results in an accumulation of tensileforce in the doctor along its length, causing one end to pull moreheavily against its anchor than the other, to an extent depending on thevalue of the static preload applied. The asymmetric loading of thedoctor results in an asymmetric positioning of it, with a helix anglewhich increases from the slack end to the taut end of it.

In the present application of this invention the drum moves while thedoctor is stationary. However, since only relative motion between thedoctored surface and the doctor is required, the drum may be fixed anddoctor may be anchored to supports which rotate about the axis of thedrum to give the required relative motion.

While the invention is directed primarily to the prevention of theaccumulation of wood fibres deposited on the surface of a steam heatedcylindrical drum rotating vertically in a tank of paper making stock, itis by no means limited to such application. There are many otherinstances where a drum surface, cylindrical or otherwise, needsdoctoring and in industries outside the field of pulp and paper. Thedoctoring device which constitutes this invention is as readilyapplicable to the drum surfaces employed in these other instances andother industries. The axis of the drum may be vertical, as described, orhorizontal, or have any other attitude, without detriment to the actionof the invention.

The combined flexibility and helical application of the doctor lendsitself to eflicient use on convex and concave surfaces of a solid ofrevolution as well as to cylindrical surfaces. In the case of a concavesurface the flexibility of the doctor will permit the doctor to liealong the surface when th helix angle is adjusted to suit the concavecurvature provided that the degree of curvature is not too pronounced.

What I claim is:

1 1. The combination with a drum or cylinder of a flexible doctoringdevice extending substantially helically around the drum or cylinder inscraping contact therewith, means for effecting relative rotary movementbetween the doctoring device and the drum or cylinder whereby materialadhering to the surface of the drum is doctored off, means fortensioning opposite ends of the doctoring device to cause the latter toengage firmly and continuously the drum or cylinder along the entirehelical line of contact between the doctoring device and the drum orcylinder, a clamping means located outwardly of opposite ends of thedrum and adapted to secure opposite ends of the doctoring device whenthe latter is under tension, said clamping means comprising a brackethaving a clamping surface disposed to lie in a plane substantiallytangential to the curved surface of the drum at the nearest point ofcontact of the doctoring device with the drum surface, a clamping barmounted on the clamping surface of said bracket to straddle thedoctoring device at right angles to the longitudinal direction of thedoctoring device between the bracket and the first point of contact withthe drum, and clamping bolts extending through said clamping bar andinto said bracket at either side of the doctoring device.

2. The combination claimed in claim 1, in which the angle of the helixof said doctoring device is variable to compensate for the loading forceto be applied by the doctor edge against the surface to be doctored.

3. The combination claimed in claim 1, in which the doctoring device isof an undefined length, a reel mounted at one end of said drum beyondsaid clamping means about which said undefined length of the doctoringdevice is coiled for intermittently feeding successive portions of thedoctoring device helically across the drum surface as preceding portionsbecome worn out;

4. The combination claimed in claim 3, in which the doctoring deviceconsists of a length of wire.

5. The combination claimed in claim 3, in which the cross section of thedoctoring device is triangular.

6. The combination claimed in claim 3, in which the doctoring deviceconsists of a tape of flexible, wear-resistant material.

7. The combination claimed in claim 3, in which the doctoring deviceconsists of a tape of flexible, wear-resistant material having at leastone bevelled, longitudinal side edge.

8. The combination claimed in claim 3, in which the doctoring deviceconsists of a tape of flexible, wear-resistant material having onesurface concavely curved to conform with that portion of the drumsurface along which the tape lies according to the predetermined angleof helix of said tape.

References Cited in the file of this patent UNITED STATES PATENTS 95,722Pond. Oct. 12, 1869 2,392,490 Maruri Jan. 8, 1946 2,664,792 Cook Jan. 5,1954 2,665,444 Nelson Jan. 12, 1954 FOREIGN PATENTS 695 Great BritainMar. 7, 1872

